Leap-frogging men to Mars

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A mission to Mars will be mankind's next giant leap.

But one expert has suggested it might be simpler to get to the red planet in a series of smaller jumps - using asteroids as stepping stones.

Professor Richard Binzel of the Massachusetts Institute of Technology is calling for a comprehensive survey of asteroids between Earth and Mars so a plan can be formulated.

"Near-Earth asteroids are the most accessible interplanetary stepping stones to Mars," said Binzel.

"Once humans can reach one asteroid in its native orbit, the gateway is opened such that hundreds, if not thousands more will be accessible.

"Thousands of shipping-sized and larger asteroids pass almost as close as the Moon each year.

"Owing to their minuscule gravity fields, a rendezvous with an asteroid merely entails sidling up and flying alongside one, with no need for a specialised landing craft."

Nasa is devising a plan to capture an asteroid with a giant claw or net and bring it closer to Earth so that astronauts could explore it.